CHEM107_PART_9_15.pdf - UNIT-09 SOLUTIONS AND...

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UNIT-09 SOLUTIONS AND CONCENTRATIONS When we mix two liquids or a solid in liquid or a gas in a gas or a solid in solid , we generate a mixture. We call this mixture a solution where the smaller amount components are solutes and the largest component is solvent CTQ-1: Consider a sugar solution: 100 grams of table sugar dissolved in 1000 grams of pure water. Is sugar solute or solvent? _________ The atmospheric air contains 78% N 2 , 20.9% O 2 , 0.9% Ar and the rest is other gases such as CO 2 , water vapor. List solute and solvent in the air solution : Solutes: _____________ Solvent:_________ POLARITY AND SOLUBILITY: Polarity of the molecules play key role in making two substances soluble. A polar molecule likes to interact with polar molecule due to dipole-dipole and other interactions we learned earlier. A non-polar molecule prefers to interact with non-polar molecule. Dispersion forces are main source of interaction energy in non-polar solutions. CTQ-2: Consider the following set of molecules. Classify them as polar (P) or non-polar (NP) molecules . CCl 4 ___ C 6 H 6 ___ H 2 O ___ C 2 H 5 OH ___ BCl 3 ___ NaCl___ NH 3 __ Create three possible non-polar solutions by mixing these compounds: 1) 2) 3) Create three possible polar solutions by mixing these compounds: 1) 2) 3)
CTQ-3: Consider the dipole-moment ( μ ) in debyes (D), of some molecules: Br 2 (μ=0) H 2 O (μ=1.87) CCl 4 (μ=0) C 6 H 6 (μ=0) NH 3 (μ=1.46) CS 2 (μ=0) Is Bromine more soluble in benzene or in water? __________ Is KCl more soluble in CCl 4 or in liquid ammonia __________ Is liquid ammonia more soluble in CS 2 or water? __________
CONCENTRATION OF SOLUTIONS As we dissolve certain solute in a solvent to make solution, how do we express or measure the amount of solute in solvent? There are three ways to express the concentration of the solution. 1. Percent by mass : the percent mass of solute in the total weight by mass of solution (solute + solvent). All masses are expressed in grams 2. Molarity : The number of moles of solute in the volume of solution (in Liters) 3. Molality : The number of moles of solute in the mass of solvent (expressed in kilograms) The formulae for the three types of concentration measurement are: HINT : Look at the definition of mola rity (M). There are three variables: M, n and V. If we know any two of these values, we should be able to calculate the third variable. Remember: Volume must be in Liters. M = 𝑛 𝑉 n = M.V CTQ-4: If 11.0 g of naphthalene, C 10 H 8 , is dissolved in 112.5 g of chloroform, CHCl 3 , what is the molality of the solution? If you need to calculate, Molarity for this problem, can you calculate? YES/NO

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